Magneto ignition systems are based upon the electrical principle that a voltage is generated in any conductor which is subjected to a change in magnetic flux through the conductor. More specifically, a sudden change of the magnetic flux in the core upon which a conductor is mounted will induce a high voltage which can be applied to a spark gap for fuel ignition.
The conventional ignition systems for internal combustion engines have used cam actuated breaker points. The breaker points physically break the magneto coil circuit to induce a high voltage at the proper time in the engine cycle to cause sparking action at the spark plug. With the advent of solid-state switching circuits, many designers in the ignition art recognized the advantages of substituting such circuits for the breaker points. Various electronic circuits, including transistors and silicon controlled rectifiers (SCR), were used in place of the breaker points to interrupt the current to the magneto or primary winding. The use of an auxiliary pick-off coil to trigger the switching action of the electronic circuit also was implemented as an appropriate means to control the timing of the switching action.
In U.S. Ser. No. 790,704, now U.S. Pat. No. 4,120,277 filed May 25, 1977 there is described a breakerless magneto device which utilizes primary and trigger windings mounted on separate cores. The core upon which the auxiliary trigger coil is mounted is located close to the main magneto core for reasons of spark timing, but is operationally substantially isolated magnetically therefrom. A thyristor and a semiconductor circuit such as Darlington connected transistors act as switching elements for interrupting the current in the primary winding of the magneto.